The installed base of solar energy power systems in general, and photovoltaic systems in particular, is growing rapidly around the world as a result of government policies and incentives, decreases in its installed cost, and increases in the cost of conventionally generated electricity. Solar irradiance is, on an annual basis, periodic and predictable. However on an hourly or sub-hourly basis, solar energy often intermittent and appears unpredictable. As an electrical generation technology solar energy has suffered the stigma, in the mainstream commercial energy community, of being unreliable and lacking the ability to be dispatched as and when it is needed. As increasing amounts of solar energy generating capacity are deployed, mechanisms are needed to reconcile the natural variations of the solar resource with the constant reliability requirements of the modern electrical grid, and energy trading requirements in those regions with deregulated energy markets. For system operators who must manage the dispatch of generation, the reserves and the transmission constraints of the grid, solar energy presents no operational problem as long as its contribution is a small percentage of the energy flowing through the system. However large amounts of solar energy, whether on the customer's side or on the supply side of the revenue meter, present a serious management challenge to the stability and reliability of the grid, as well as to the transactions of energy markets. Several recent technological developments are brought together in this technology that make it possible to forecast ground level irradiance, and thus solar energy production, across a region or utility service territory.